Influence of select bioenergy by-products on soil carbon and microbial activity: A laboratory study.

Concerns about the negative impacts of crop biomass removal on soil ecological functions have led to questioning the long-term sustainability of bioenergy production. To offset this potential negative impact, use of organic C rich by-products from the bioenergy industries have been proposed as a means to replenish soil C in degraded soils. However, the impact of these by-products application on soil carbon dynamics is not fully understood. We measured biogeochemical changes in soil organic C following a three-year field application of two by-products, biochar (BC) and fermentation-by product (FBP), of bioenergy industry processes in an elephant grass [Pennisetum purpureum (L.) Schum.] field. There was a significant increase in overall soil organic C (SOC) observed in BC (270%) treated plots, however the higher labile SOC (51%) content was present in FBP treated plots. Solid-state 13C NMR spectroscopy further revealed increased aromatic and alkyl groups in BC amended soils which lend to its significantly higher hydrophobicity index, HI (2.13) compared with FBP amended soils (HI = 0.8). Initial biogeochemical responses of amended soils to drought conditions were also investigated during a short-term experiment with drying and rewetting of soils. Increased concentrations of extractable C and higher stimulation of microbial activities (respiration and enzyme activities) in FBP amended soils were measured. Overall, our results reveal different impacts of the two soil amendments, where FBP soil application can affect the labile SOC availability, and stimulate rapid microbial response in drought affected soils, and biochar soil application lowers the labile SOC and microbial stimulation facilitating C sequestration over time.

Clostridium chromiireducens sp. nov., isolated from Cr(VI)-contaminated soil.

A Cr(VI)-resistant, Gram-positive, spore-forming, obligate anaerobe, designated GCAF-1(T), was isolated from chromium-contaminated soil by its ability to reduce Cr(VI) in low concentrations. Mixed acid fermentation during growth on glucose resulted in accumulation of acetate, butyrate, formate and lactate. Morphological studies indicated the presence of peritrichous flagella, pili and an S-layer. The major cellular fatty acids (>5 %) were C(16 : 0), C(14 : 0), summed feature 3 (comprising iso-C(15 : 0) 2-OH and/or C(16 : 1)ω7c), C(18 : 1)ω7c, C(16 : 1)ω9c, summed feature 4 (comprising iso-C(17 : 1) I and/or anteiso-C(17 : 1) B) and C(18 : 1)ω9c. The DNA G+C content of strain GCAF-1(T) was 30.7 mol%. Phylogenetic interference indicated that strain GCAF-1(T) clustered with group I of the genus Clostridium. Of strains within this cluster, strain GCAF-1(T) shared the highest 16S rRNA gene sequence similarities (98.1-98.9 %) with Clostridium beijerinckii DSM 791(T), C. saccharobutylicum NCP 262(T), C. saccharoperbutylacetonicum N1-4(T), C. puniceum DSM 2619(T) and C. roseum DSM 51(T). However, strain GCAF-1(T) could be clearly distinguished from its closest phylogenetic neighbours by low levels of DNA-DNA relatedness (<50 %) and some phenotypic features. Based on the evidence presented here, strain GCAF-1(T) ( = DSM 23318(T) = KCTC 5935(T)) represents a novel species of the genus Clostridium, for which the name Clostridium chromiireducens sp. nov. is proposed.